It is becoming increasingly evident that the opiates, under certain conditions, can produce effects that far outlast their period of administration. The proposed research intends to determine the long lasting effects of exposure to morphine sulfate, during in utero development, on a number of neuroendocrine processes after birth. Basal circulating levels of anterior pituitary hormones (luteinizing hormone, prolactin, thyroid stimulating hormone and growth hormone) will be compared between control pups and offsprings of rats exposed to morphine from day 5 through day 12 of gestation. Growth rate as well as the timing of the onset of puberty will also be recorded in these animals. Response of the animal to opiate agonists and antagonists, in terms of analgesia and hormone release, will be compared between controls and those born to morphine-treated mothers. Finally the opiate receptor number will be determined in rats exposed to morphine during in utero development. It is also proposed that the influences of morphine treatment, during pregnancy, on the dam will be examined. The parameters to be studied will include maintenance of gestation, circulating hormone levels before and after delivery, the milk-ejection reflex and the onset of first estrus.